Hi @Mark Ward,
Thanks for reaching out.
I am able to replicate this issue in my test tenant. As per my analysis, there is delay reflecting the changes from OneNote UI to Graph API response as it relies on indexing service in the backend.
Can you check the same Graph API response after few minutes the change from OneNote UI?
If you are still facing the same issue with some delay, I would recommend you to raise a support case with Microsoft Graph, a Support Engineer will be able to assist you better. You can raise support ticket from https://aad.portal.azure.com/ or https://admin.microsoft.com/#/support/requests.
Hope this helps.
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